This invention relates to the separation of the formed elements, i.e., white cells, red cells and platelets of blood, from the serum or plasma of the blood.
Such separation is typically performed by centrifuging a blood sample in a collection tube such that the heavier formed elements of the blood are forced to the bottom or closed end of the collection tube and the lighter plasma or serum of the sample remains on top or toward the open end of the collection tube.
After such separation by centrifugation, it is desirable to physically separate the formed elements of the blood from the serum or plasma in order to prevent the contamination of the serum or plasma. Such contamination can occur as the red blood cells begin to liberate potassium and other contaminants which might interfere with tests performed on the serum or plasma. It is also possible that any fibrin which remains in the sample may, produce some contamination.
In order to achieve this isolation or fluid separation of the formed elements of the blood from the serum or plasma, separator tubes have been utilized. The separator tubes which are adapted to be inserted into a collection tube typically comprise a tubular member having one end closed by a plug which is formed from an elastomeric material. The plug includes a centrally located one-way valve which is forced open as the separator tube is forced downwardly through a blood sample in a collection tube so as to allow the serum or plasma to flow into the separator tube. When the separator tube becomes stationary relative to the collection tube i.e., just before contact with the formed elements of the blood, the one-way valve closes so as to isolate the plasma within the separator tube. The separator tube may then be withdrawn.
It has been found to be particularly desirable to utilize the separator tube in and of itself as a transport device for transporting the serum or plasma to the laboratory from the point at which the blood sample is taken. This requires that the one-way valve at the closed end of the separator tube be essentially leak-proof. My U.S. Pat. Nos. 3,661,265 and 3,799,342 disclose a substantially leak-proof valve which does permit the use of the separator tube as a transport device. The one-way valve disclosed therein essentially relies upon the elastomeric properties of the plug to return the valve to the closed condition, i.e., there is no force or bias acting on the valve when the separator tube is in the stationary position and the valve is closed. Rather, the valve elements, when properly structured, merely contact one another when returning to a natural or unbiased state in which they were originally molded. Proper closure of these valves may be assisted by the tubular member if the inside diameter of the tubular member is slightly smaller than the outside diameter of the plug but the tolerances on the inside diameter of the tubular member are difficult to control particularly where the tubes are extruded.
U.S. Pat. No. 3,954,614 also discloses a valve in a separator tube which is characterized by little or no seating forces when the valve is in the closed position. The same is true with respect to U.S. Pat. No. 3,962,085 wherein the periphery of a disc acts as a valve which is closed when the disc is in the closed position. However, there are no substantial seating forces beyond weight of the blood sample itself. Valves such as those shown in U.S. Pat. Nos. 1,777,408 and 2,191,636 are biased so as to provide a substantial sealing force when in the closed position, but such valves are too complex for use in serum separators.